Metal tooling or "tools" of the type with which the present invention is concerned are used during fabrication of parts, particularly parts of composite materials for aircraft. Such parts may be large or small, essentially flat or abruptly contoured, and structural or nonstructural. Examples are composite structural spars and ribs, large ducts, and interior panels. In each instance, the material to be formed is laid up on or otherwise applied to the metal tool, and then cured by application of heat or heat and pressure.
In the aircraft industry, tools of the type with which the present invention are concerned usually fall within one of the following categories:
(1) lay up mandrels for large composite parts, which can range from a few inches in length to 30 or 40 feet or more in length;
(2) compression mold dies;
(3) molds for vacuum forming; and
(4) rotary molding tools.
Lay up mandrels and compression mold dies typically are subjected to temperatures of about 350.degree. F. during fabrication of the part, and then are cooled down to approximately room temperature. Vacuum forming molds are subjected to temperatures of up to about 400.degree. F. Rotary molding tools are subjected to temperatures of up to about 600.degree. F. In each instance, the tools are cooled, preferably rapidly, for the next part forming operation. Such tools can sustain surface damage due to normal wear and tear, or abnormal surface damage during transport or while in service. More frequently, the tool may be fabricated with under-dimensioned surfaces, such as due to computer numerically controlled (CNC) machining errors.
In the past, repairs performed on under-dimensioned or damaged metal tools used materials such as epoxies and cement fillers, resulting in very short service life due to vast differences in material properties and the extreme temperatures, pressures, and operations to which the tools were subjected. Other repair techniques included weld filling, i.e., laying up weld beads followed by machining, which necessarily involves application of localized heat. This typically augmented the problem area as dimensional problems would crop up due to warping. Another known repair technique referred to as "tearing and salvaging" (removing large sections of the problem area and refabrication) may require securing a refabricated area or component to the remainder of the part by welding, and thereby introducing a new dimensional problem in the welded area.
Conventional rework methods often are not successful, and the tool must be scrapped.